.\" $OpenBSD: X509_STORE_CTX_set_verify.3,v 1.8 2024/06/07 05:51:39 tb Exp $
.\"
.\" Copyright (c) 2021, 2022 Ingo Schwarze <schwarze@openbsd.org>
.\" Copyright (c) 2023 Job Snijders <job@openbsd.org>
.\"
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.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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.Dd $Mdocdate: June 7 2024 $
.Dt X509_STORE_CTX_SET_VERIFY 3
.Os
.Sh NAME
.Nm X509_STORE_CTX_verify_fn ,
.Nm X509_STORE_CTX_set_verify ,
.Nm X509_STORE_CTX_get_verify ,
.Nm X509_STORE_set_verify ,
.Nm X509_STORE_set_verify_func ,
.Nm X509_STORE_get_verify ,
.Nm X509_STORE_CTX_check_issued_fn ,
.Nm X509_STORE_set_check_issued ,
.Nm X509_STORE_get_check_issued ,
.Nm X509_STORE_CTX_get_check_issued
.Nd user-defined certificate chain verification function
.Sh SYNOPSIS
.In openssl/x509_vfy.h
.Ft typedef int
.Fo (*X509_STORE_CTX_verify_fn)
.Fa "X509_STORE_CTX *ctx"
.Fc
.Ft void
.Fo X509_STORE_CTX_set_verify
.Fa "X509_STORE_CTX *ctx"
.Fa "X509_STORE_CTX_verify_fn verify"
.Fc
.Ft X509_STORE_CTX_verify_fn
.Fo X509_STORE_CTX_get_verify
.Fa "X509_STORE_CTX *ctx"
.Fc
.Ft void
.Fo X509_STORE_set_verify
.Fa "X509_STORE *store"
.Fa "X509_STORE_CTX_verify_fn verify"
.Fc
.Ft void
.Fo X509_STORE_set_verify_func
.Fa "X509_STORE *store"
.Fa "X509_STORE_CTX_verify_fn verify"
.Fc
.Ft X509_STORE_CTX_verify_fn
.Fo X509_STORE_get_verify
.Fa "X509_STORE_CTX *ctx"
.Fc
.Ft typedef int
.Fo (*X509_STORE_CTX_check_issued_fn)
.Fa "X509_STORE_CTX *ctx"
.Fa "X509 *subject"
.Fa "X509 *issuer"
.Fc
.Ft void
.Fo X509_STORE_set_check_issued
.Fa "X509_STORE *store"
.Fa "X509_STORE_CTX_check_issued_fn check_issued"
.Fc
.Ft X509_STORE_CTX_check_issued_fn
.Fo X509_STORE_get_check_issued
.Fa "X509_STORE *store"
.Fc
.Ft X509_STORE_CTX_check_issued_fn
.Fo X509_STORE_CTX_get_check_issued
.Fa "X509_STORE_CTX *ctx"
.Fc
.Sh DESCRIPTION
.Fn X509_STORE_CTX_set_verify
configures
.Fa ctx
to use the
.Fa verify
argument as the X.509 certificate chain verification function instead
of the default verification function built into the library when
.Xr X509_verify_cert 3
is called.
.Pp
The
.Fa verify
function provided by the user is only called if the
.Dv X509_V_FLAG_LEGACY_VERIFY
or
.Dv X509_V_FLAG_NO_ALT_CHAINS
flag was set on
.Fa ctx
using
.Xr X509_STORE_CTX_set_flags 3
or
.Xr X509_VERIFY_PARAM_set_flags 3 .
Otherwise, it is ignored and a different algorithm is used that does
not support replacing the verification function.
.Pp
.Fn X509_STORE_set_verify
saves the function pointer
.Fa verify
in the given
.Fa store
object.
That pointer will be copied to an
.Vt X509_STORE_CTX
object when
.Fa store
is later passed as an argument to
.Xr X509_STORE_CTX_init 3 .
.Pp
.Fn X509_STORE_set_verify_func
is an alias for
.Fn X509_STORE_set_verify
implemented as a macro.
.Pp
.Fn X509_STORE_set_check_issued
saves the function pointer
.Fa check_issued
in the given
.Fa store
object.
That pointer will be copied to an
.Vt X509_STORE_CTX
object when
.Fa store
is later passed as an argument to
.Fn X509_STORE_CTX_init 3 .
.Pp
The
.Fa check_issued
function provided by the user should check whether a given certificate
.Fa subject
was issued using the CA certificate
.Fa issuer ,
and must return 0 on failure and 1 on success.
The default implementation ignores the
.Fa ctx
argument and returns success if and only if
.Xr X509_check_issued 3
returns
.Dv X509_V_OK .
It is important to pay close attention to the order of the
.Fa issuer
and
.Fa subject
arguments.
In
.Xr X509_check_issued 3
the
.Fa issuer
precedes the
.Fa subject
while in
.Fn check_issued
the
.Fa subject
comes first.
.Sh RETURN VALUES
.Fn X509_STORE_CTX_verify_fn
is supposed to return 1 to indicate that the chain is valid
or 0 if it is not or if an error occurred.
.Pp
.Fn X509_STORE_CTX_get_verify
returns a function pointer previously set with
.Fn X509_STORE_CTX_set_verify
or
.Xr X509_STORE_CTX_init 3 ,
or
.Dv NULL
if
.Fa ctx
is uninitialized.
.Pp
.Fn X509_STORE_get_verify
returns the function pointer previously set with
.Fn X509_STORE_set_verify ,
or
.Dv NULL
if that function was not called on the
.Fa store .
.Pp
.Fn X509_STORE_get_check_issued
returns the function pointer previously set with
.Fn X509_STORE_set_check_issued ,
or
.Dv NULL
if that function was not called on the
.Fa store .
.Pp
.Fn X509_STORE_CTX_get_check_issued
returns the
.Fn check_issued
function pointer set on the
.Vt X509_STORE_CTX .
This is either the
.Fn check_issued
function inherited from the
.Fa store
used in
.Xr X509_STORE_CTX_init 3
or the library's default implementation.
.Sh SEE ALSO
.Xr X509_check_issued 3 ,
.Xr X509_STORE_CTX_init 3 ,
.Xr X509_STORE_CTX_set_error 3 ,
.Xr X509_STORE_CTX_set_flags 3 ,
.Xr X509_STORE_CTX_set_verify_cb 3 ,
.Xr X509_STORE_new 3 ,
.Xr X509_STORE_set_flags 3 ,
.Xr X509_STORE_set_verify_cb 3 ,
.Xr X509_verify_cert 3 ,
.Xr X509_VERIFY_PARAM_set_flags 3
.Sh HISTORY
.Fn X509_STORE_set_verify_func
first appeared in SSLeay 0.8.0 and has been available since
.Ox 2.4 .
.Pp
.Fn X509_STORE_CTX_set_verify
and
.Fn X509_STORE_CTX_get_verify
first appeared in OpenSSL 1.1.0 and have been available since
.Ox 7.1 .
.Pp
.Fn X509_STORE_CTX_verify_fn ,
.Fn X509_STORE_set_verify ,
and
.Fn X509_STORE_get_verify
first appeared in OpenSSL 1.1.0 and have been available since
.Ox 7.2 .
.Pp
.Fn X509_STORE_set_check_issued ,
.Fn X509_STORE_get_check_issued ,
and
.Fn X509_STORE_CTX_get_check_issued
first appeared in OpenSSL 1.1.0 and have been available since
.Ox 7.3 .
.Sh BUGS
The reversal of order of
.Fa subject
and
.Fa issuer
between
.Fn check_issued
and
.Xr X509_check_issued 3
is very confusing.
It has led to bugs and will cause many more.
